Arrangement of noninductive terminals for variable condensers



Nov. 26, 1940. A. c. DUCATI 2,223,061

ARRANGEMENT OF NONINDI IGTIVE TERMINALS FOR VARIABLE CONDENSERS FiledDec. 20, 1937 Qdriano Cawlieri Ducafz' ATTORNEYS Patented Nov. 26, 1940UNITED STATES ARRANGEMENT OF NONINDUCTIVE TER- MINALS FOR VARIABLECONDENSERS Adriano Cavalieri Ducati, Bologna, Italy Application December20, 1937, Serial No. 180,854 In Italy December 19, 1936 2 Claims.

(Granted The present invention relates to precision electrostaticcondensers and more particularly relates to a system of terminals forvariable electrostatic condensers minimizing the inductance 75v orinductive reaction for the electrical connection to the condensers.

The greatest value of a precision variable condenser such as is employedin laboratories or in electrical measurements or comparisons isconstancy of its capacity over a great range of applied frequency. Thecapacity of a precision variable condenser depends upon its inherentcapacity which can be determined to a fraction of a micro-microfarad.However, the effective capacitance of the condenser depends also to somedegree upon the frequency of the applied signal. The inherent inductancein the condensers of the prior art caused a variation in the effectivecondenser capacitance which changed with the frequency applied thereto,the higher the frequency range, the greater the variation in theeffective capacitance of the condenser and therefore its determinableaccuracy.

The inherent inductance of a. precision variable condenser is veryimportant, particularly at the higher frequency such as in radiofrequency or ultra-high frequency use, even though its value may be aone-hundredth or smaller part of a microhenry. I have found that theterminal con- 80 nections to the variable condenser produce the greaterportion of the inductance of the condenser, and it is among the objectsof my present invention to minimize the inductive reaction of thecontacts to the variable condenser.

In accordance with my present invention, I contemplate arranging theterminal connections to the plates thereof in a manner to nullify orgreatly minimize the inductance thereof as compared to the prior artcondensers. In one form 40 of the invention, I provide the terminals tothe stationary and rotary plates of the condenser concentricallyarranged whereby any self-inductive reaction of any one terminal iscancelled or nullified by that of the other one. In a modi- 45. ficationof my invention I provide two closely adjacent terminal posts adapted togreatly minimize the inductive reaction of the connection to thecondenser plates. By thus minimizing the inductance of the variablecondenser, the capa- 50 city thereof remains more constant over a muchgreater frequency range than the condensers of the prior art.

It is accordingly an object of my present invention to provide a novelsystem of terminal con- 55 tacts for a variable condenser.

It is another object of my present invention to provide a novelarrangement for connection to the stator and rotor plates of a precisionelectrostatic condenser.

It is still another object of my present invenunder the provisions ofsec. 14, act of March 2, 1927; 357 0. G.

tion to materially minimize the inherent inductance of variableelectrostatic condensers.

These and further objects of my present invention will become apparentin the following description taken in connection with the draw- 1 ing inwhich:

Figure 1 is an end view of a preferred construction of a variablecondenser in accordance with my present invention with the turning knobomitted and represents the View taken along ll in Figure 2.. v

Figure 2 is a plan view of the condenser shown in Figure 1.

Figure 3 is a perspective view partly in section of a modified form ofmy present invention.

Figure 4 is a schematic view of still a further form of my invention.

Figure 5 is a diagrammatic illustration of the principle embodied in myinvention.

' In Figure 1 I have illustrated a semi-circular type condenserconstruction comprising the fixed or stator portion and rotatable orrotatorportion II'. The stator portion I6 is affixed or mechanicallysecured to the terminal or contact rod I 2, together with the stud 13 asshown in Figures 1 and 2. The rotor section II is centrally secured tothe rod I l together with the stud IS. A knob l8 may be affixed at theprojecting end of the terminal post M as shown in Figure 2. The rods l2and I4 may be of small diameter and of solid metallic conductingmaterial such as aluminum, copper or the like, or may well be hollow ortubular in accordance with principles of design for minimizing condenserlosses well known in the art.

In accordance with the principle of my present invention, thedisposition of the rotor and stator plates l0 and II and the terminalposts [2 and M respectively are arranged whereby the terminals l2 and I4may be as physically close together as possible, more so than any of thecondensers of the prior art. As will be hereinafter pointed out, suchclose disposition of the terminal rods [2 and I4 parallelly arranged asseen in Figure 2 makes for a constancy of capacity for the unit with aminimum of inherent inductance.

In order to provide for a 180 rotation for the rotor I l in thepreferred physical arrangement as described and without mechanicallyinterfering with the terminal post l2 of the stator 10, the cut-awaysection H5 in the rotor plate ll obviates the mechanical interferencebetween the rotor plates II and the post [2 as will now be evident. Ifurther provide a cut-away'portion I! in the stator plate, to permitcloser positioning between the posts l2 and I4 and avoid the necessaryprojecting portion of the stud l5 and post H as will also now beevident. Accordingly, it is to be understood that the design of thecondenser plates Ill and H with the provided cutaway sections IE and IIare for permitting as physically close positioning of the terminal postsl2 and I4 as practicable and furthermore permit a full 180 rotation ofthe rotor section ll of the condenser. It is to be further understoodthat the illustrations I have made are with a single plate rotor andsingle plate stator for simplicity of illustration and that a pluralityof such plates may be used with the modifications I have described aswill beevidentto those skilled in :the art; Terminal leads I9 areconnected to the extremity of the parallel terminal rods l2 and 54. Thenon-inductive arrangement of the flexible leads |9 may be arranged inany manner known in the art, the present invention being particularlyconcerned with the minimizing of inductive reaction of the electricalcondensers per se.

A modified form in applying my invention to variable condenserconstruction is illustrated in Figure 3 wherein a fixed or stator platesection 20 is arranged opposite the rotor plate 2| adapted to be rotatedby the central connection rod 24 to which it is secured, A knob 28 ispreferably aflixed to a projection of the central rod 24 as shown in thefigure. The knob 28 is naturally of insulation material to permithandling by the operator.

The stator 20 is secured to a metallic tube 22 which is concentric aboutand co-extensive with the central rotor connection rod 24. It is to beunderstood that the tube 22 preferably completely surrounds the rod 24and is broken away in the illustration. Insulation bushings 25electrically separate and maintain the connection posts 22 and 24 inproper mechanical and electrical relation. The wire-leads 29 connect tothe terminal rods 22 and 24 as shown to connect the condenser to thenecessary electrical circuits.

to prevent mechanical interference between the v ure is included toillustrate this principle.

rotor 3| and the terminal rod 33 of the stator plate 30. The terminalrod 34 of the rotor plate 3| is adapted to be secured to a knob or otherelement for rotation. It is to be understood that the mechanicaldisposition of the terminal rods 33 and 34 are similar to thehereinabove described arrangement in connection with Figures 1 and 2 ofrods l2 and M to cause minimum inductive action by the terminal rods.

The principle of minimizing the inherent inductance vof the terminalconnections for the variable condensers of my present invention ispredicated upon the phenomena of minimizing inductance by arranging twoconductors in parallel and in close juxtaposition and in causing similarcurrents to fiow therein in opposite directions. The schematic diagramforming Fig- The two conductors 40 and 4| are arranged in parallel.These conductors may be the opposite plates of a condenser or may wellrepresent the parallel terminal rods I2 and I4 of Figure 2; or 22 and 24of Figure 3. The horizontal arrows represent the direction of thecurrent i flowing therein. The current i in the conductors 40 and 4| arenecessarily of substantially equal value due to the series relation. Thetransverse arrows between theplates Mland 4| represent; the capacitiverelation or reaction C between these plates or conductors which, being ageometric entity is substantially constant .for wide frequency ranges. V

I have placed corresponding arrows upon the Figures 2 and 3 to representthe direction of flow of the currents in the parallel terminal contactsand condenser plates to indicate how the principle of minimizing theinductive reaction of them is effected by my invention.

It is to be understood that the terminal rods of the condensers arearranged to be placed as close together as possible to minimize as muchas possible the inductive reaction thereof as will now be understood bythose skilled in the art. The cut-away portions illustrated in some ofthe modifications permit close positioning of the terminal rods. In themodification of Figure 3, the concentric relation of the terminal rodsaffords the theoretical minimum of inductance therefor. My invention isapplicable for all types of variable condensers irrespective of theirshape or. use and is designed to minimize the inherent inductancetherein to provide. a substantially constant effective capacitance ofthe condenser over wide frequency ranges and particularly for high radiofrequency precision measurements.

Having described particular embodiments of my invention, modificationswhich fall within the broader spirit and scope of my invention may beevident to those skilled in the art and accordingly, I do not intend tobe limited except as set forth in the following claims.

I claim:

1. A high frequency precision variable condenser comprising a statorsection of substantially semi-circular shape, a rotor section ofsubstantially semi-circular shape, a terminal rod secured solely to oneregion of said rotor adapted to rotate saidrotor, a second terminal rodsecured solely toone region of said stator, said rods being parallel andarranged mechanically close for minimizing the inductive reactionthereof, said rotor section having a cut-away portion to permit theclose positioning of said rods and full effective one-hundred and eightydegree rotation of said rotor, whereby the fiow of high frequencycurrent in the condenser through said rods, rotor and statorsubstantially cancel inductive reaction therein to provide a stableefiective capacitance for the condenser when operated at highfrequencies.

2. A high frequency precision variable condenser comprising a statorsection of substantially semi-circular shape, a rotor section ofsubstantially semi-circular shape, a terminal rod secured solely to oneregion of said rotor adapted to rotate said rotor, a second terminal rodsecured solely to one region of said statonsaid rods being parallel andarranged mechanically close ,for minimizing the inductive reactionthereof, said rotor section having a cut-away portion to permit theclose positioning of said rods and full effective one-hundred and eightydegree rotation or said rotor, said stator having a cut-away portionopposite the position of said rotor, and said second rod beingasymmetrically placed on the stator, whereby the flow of high frequencycurrent in the condenser through said rods, rotor and statorsubstantially cancel inductive reaction therein to provide a stableeffective capacitance for'the condenser when operated at highfrequencies.

ADRIANO' CAVALIERI DUCATI.

